In recent years, addition of various nanomaterials has been studied for purposes of downsizing and weight saving in various fields. In particular, for problems of environments or resources, carbon materials such as graphene, CNT and fullerene have attracted attention as nonmetal nanomaterials. For example, a lithium-ion battery currently put to practical use has been improved in its capacity owing to an improvement of the active material itself. However, the capacity is significantly lower than its theoretical capacity, and further improvement has been desired.
Regarding this matter, while acetylene black has been conventionally used as a conductive assistant for lithium-ion batteries, novel high conductive materials such as a carbon nanofiber (VGCF (vapor grown carbon fiber): registered trademark) manufactured by Showa Denko K. K. have been studied in recent years to further improve electrical conductivity (Patent Literature 1: JP-A-2013-77475).
Further, a method of improving cycle characteristics (repetition performance) of a battery by directly coating a positive electrode active material with an electrical conductor and a method of producing a high-capacity and high-output lithium-ion battery by focusing attention on ion conductivity have been studied. (Patent Literature 2: JP-T-2013-513904), (Patent Literature 3: WO 2014/115669)
Furthermore, nanosizing of an active material itself for a lithium-ion battery has been also studied in recent years. (Non-Patent Literature 5)